Medical devices such as pacemakers, stimulators or drug delivery systems are typically implanted subcutaneously; this minimizes the invasiveness of the procedure and facilitates access, whether by electrical coupling (e.g. for charging or telemetry) or physically (e.g. needle access). Implantation may be rather like stowing a Jack-in-the-box, in that during and even after implantation, the medical device may at any moment pop out of the subcutaneous pocket in which it is implanted. Such devices commonly have leads or catheters coiled behind or beneath them, like the spring in such a Jack-in-the-box toy.
A related problem is that following implantation, the device may flip over. Even after encasement in an envelope of fibrous scar tissue, unless it is constrained it retains this potential. If it is a pump with a refill port on one side, or an electronic implant with a charging or telemetry coil on one side, this can render it nonfunctional. If it flips over repeatedly, it may twist the lead or catheter to the point that it kinks, breaks, pulls out at its distal end, or otherwise fails.
FIGS. 1-7 (PRIOR ART) show a typical implant 10. Implantable medical devices, such as by way of non-limiting example electrical stimulation devices, which typically have multicontact leads attached, accordingly have a plastic header/connector assembly 12 as shown in the Figures; implanted drug delivery systems and pumps, which typically have simple catheter connections, may not have a separate header. Plastic headers and housings typically have one or more holes 14 drilled through them, and metal “can” enclosures may have metal suture loops attached. These holes and loops accept sutures, which are placed through tissue around the implant and then tied, holding the implant in position.
FIG. 3 shows a side, cross-section view of a typical subcutaneous pocket formed during surgical implantation. The pocket 20 is typically created on one side, and not both sides, of the surgical incision 22. Thus when the incision is closed, typically by suturing with a suture 24 and needle 26, the wound closure is not directly over the implanted device. This avoids pressure from the device directly on the healing wound, which might cause it to break down; and it increases the path length from the device to the surface, reducing the risk of drainage from or egresss through the wound or ingress of contamination from the outside. The thickness of tissue alongside, rather than over the device, facilitates a secure closure in multiple layers.
FIG. 4 shows the common current practice of coiling redundant loops of lead or catheter 30 behind the implant 10, and then suturing the header to subcutaneous tissues. This serves the dual purpose of containing the coils and securing the implant, so that (1) during closure the coils are out of the way, and (2) after closure the implant remains secure against movement, including extrusion through the wound as well as flipping over, with coils behind it. To the extent the coils remain mobile, they provide strain relief when traction is applied to the lead by patient movement.
As shown in FIG. 5-6, radiusing the suture holes 14 to accommodate curved needles 26, with as pronounced a curve and as large a diameter as the surgeon might reasonably choose, facilitates suture placement. (Many current devices have a small straight hole which impedes passage of a curved needle, as shown in FIG. 7.) A silicone rubber plug might fill a larger hole to stabilize the suture during implantation and control tissue ingrowth afterwards.
Asymmetry about the axis of the emerging lead or catheter tends to resist flipping over, once the implant is encapsulated in scar. If the lead or catheter emerges tangentially, the implant is not as free to rotate around it, as it would be if it emerges radially, similar to the stick on a lollipop.
Notwithstanding these prior art configurations, there remains a need in the art to provide for the secure attachment of an implantable medical device within a subcutaneous pocket that may be performed without requiring extraordinary testing on the part of the surgeon.